1. Field of the Invention
The present invention relates to an inner rotor having excellent corrosion resistance, which has an outer gear serving as a component of an internal gear pump, and an outer rotor having excellent corrosion resistance, which has an inner gear engaging with the outer gear. In particular, the present invention relates to an inner rotor and an outer rotor that are made of Cu—Ni-based sintered copper alloy.
2. Description of the Related Art
In general, it has been known that an internal gear pump includes an inner rotor having an outer gear and an outer rotor having an inner gear which engages with the outer gear, and the inner rotor and outer rotor are incorporated in the internal gear pump. Furthermore, it has been known that the internal gear pump has a structure for sucking fuel from a suction port so as to discharge from a discharging port by increasing or decreasing the capacity of a pump chamber formed between contacting portions of the respective rotors by rotation of the outer rotor, which engages with the inner rotor, rotating in the same direction as the inner rotor by driving the inner rotor by a motor.
Since the structure of the internal gear pump is relatively simple and pump efficiency thereof is high, the internal gear pump has been employed in a mechanism for supplying fuel such as gasoline or light diesel oil to the engine of an automobile or the like. The inner rotor and outer rotor configuring the internal gear pump for supplying fuel is generally made of an iron-based sintered alloy, (for example, see JP-A-8-144964).
However, often, sulfur, a compound thereof, or an organic acid, such as formic acid or acetic acid, in addition to alcohol or water, may be further mixed into the diesel oil or foreign gasoline. If using the above-described inferior gasoline is used, the inner rotor and outer rotor made of iron-based sintered alloy excessively corrode. If the inner rotor and outer rotor become corroded, a contacting portion between the inner rotor and outer rotor and a junction portion between the respective rotors and a housing become worn away, so that the liquid-tight property of the pump chamber cannot be maintained. For this reason, the following problem occurs when gasoline leaks to the neighboring low pressure pump from a pump chamber, which should discharge gasoline at the high-pressure state, through the worn portion, which reduces the pump efficiency, causing the life span to be short. In order to prevent corrosion of the inner rotor and outer rotor made of the above-described related art iron-based sintered alloy, the inner rotor and outer rotor thickly plated with nickel has been proposed. The inner rotor and outer rotor have a corrosion resistance to some extent due to the thick plating of nickel, but the operation for thickly plating the rotors with nickel increases the cost. Accordingly, it is not possible to satisfy the demand for reduction in cost.